DSC PC560

I've tried to install an alarm system based on DSC PC-560 unit with 4 DSC motion sensor. The problem is that the function of the sensors seems to be reversed (no motion means close link, motion detected means open link), so I can't arm the system. The motion sensor has only 2 jumpers, one for ON/OFF led and the other for slow/fast pulses.I suppose that the central unit PC-560 should be programmed to work with "reversed logic sensor" but I don't know how.Is there anyone can help me?Thanks.